Method of operation when hot straightening elongated workpieces

ABSTRACT

An improvement in a method of hot straightening workpieces as described in U.S. Pat. Nos. 3,598,665 and 3,631,698 whereby a workpiece is inductively heated and, at the same time, the induction currents in the workpiece generate, together with the inductor current, a force thrusting the workpiece against stops advanced for that purpose. In order to avoid reduction in reverse bending and/or tortional strength, according to the method of this invention the stops are advanced into contact with the workpiece only after at least 75 percent and preferably 85 percent of the total energy required for heating the workpiece has already been supplied.

Seulen et al.

1*Jan. 15, 1974 METHOD OF OPERATION WHEN HOT STRAIGHTENING ELONGATED WORKPIECES Inventors: Gerhard Seulen; Friedhelm Reinke,

both of Rernscheid, Germany AEG-Elotherm GmbH, Remscheid-Hasten, Germany Assignee:

Notice: The portion of the term of this patent subsequent to Aug. 10, 1988, has been disclaimed.

Filed: June 5, 1972 Appl. No.: 259,663

Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 3,598,665 8/1971 Seulen et a1. 148/131 Primary Examiner-Richard J. Herbst AtzorneyJohn W. Malley et a1.

[ 5 7 ABSTRACT An improvement in a method of hot straightening workpieces as described in US. Pat. Nos. 3,598,665 and 3,631,698 whereby a workpiece is inductively heated and, at the same time, the induction currents in the workpiece generate, together with the inductor current, a force thrusting the workpiece against stops advanced for that purpose. 1n order to avoid reduction in reverse bending and/or tortional strength, according to the method of this invention the stops are advanced into contact with the workpiece only after at least 75 percent and preferably 85 percent of the total energy required for heating the workpiece has already been supplied.

6 Claims, 2 Drawing Figures METHOD OF OPERATION WHEN HOT STRAIGHTENING ELONGATED WORKPIECES The invention relates to a method of hot straightening elongated workpieces having a longitudinal axis and consisting of a non-ferromagnetic or a ferromagnetic material which for the purpose of effecting the hot straightening process is at least partly heated to a temperature above the Curie point.

One apparatus and method of hot straightening are described in U.S. Pat. Nos. 3,598,665 and 3,631,658 and advantageously serves for hot straightening and simultaneously inductively surface-hardening workpieces that are intended in use to be sujected to considerable mechanical loads, such as axles, shafts, rods and pushrods, as required, for instance, in the manufacture of motor vehicles.

The method of operation described in the abovementioned patents, the disclosure of which is explicitly incorporated herein by reference, comprises mounting the ends of the workpiece and rotating the same about its longitudinal axis, inducing in the workpiece, by means of an inductor having heating conductors extending parallel to the workpiece axis currents of a magnitude and frequency suitable for at least raising the temperature of at least part of the workpiece to the level required for hot straightening, these currents and the currents induced thereby interacting to create a magnetic field which in turn generates electromagnetic forces acting between the inductor and the workpiece.

in the case of non-ferromagnetic workpieces, the direction of these forces is such that they cause repulsion between the inductor and the workpiece. In the case of ferromagnetic workpieces the said forces first give rise to attraction between the inductor and the workpiece. However, as the inductive heating effect involves more and more parts of the workpiece and raises their temperatures above the Curie point, the direction of action of the magnetic forces reverses so that finally the workpiece responds to the forces acting upon it as if it were made of a non-ferromagnetic material.

For the generation of a straightening effect, it has already been proposed in the above-mentioned patents to provide, on the side of the workpiece facing away from the inductor, straightening abutments which can be adjusted towards the workpiece into a position in which they will be in contact with the workpiece when it is straight, so that the above-mentioned electromagnetic forces to press the workpiece against the straightening abutments. When the electric power supply is cut off, the workpiece preferably continues to be rotated and-while maintaining contact with the straightening abutmentsit is then cooled by quenching for the purpsoe of being surface-hardened. In the case of workpieces that are very badly bent, it is preferred not to adjust the straightening abutments until a certain heating time has clasped.

This delay in bringing the straightening abutments into engagement according to the above-mentioned patents is regarded as a drawback of the straightening process that must be accepted in the case of workpieces that are badly distorted.

The applicants have now found that if the method according to the above-mentioned patents is performed by adjusting the straightening abutments towards the workpiece not later than at the end of a relatively short heating time, the straightening process as such, by virtue of the straightening action taking place when the workpiece core has been only moderately heated, leaves a remanent state of stress in the workpiece, which reduces its reverse bending strength and/or its torsional strength.

The problem that underlies the present invention is the provision of a method of operation according to the above-mentioned patents that will substantially avoid any such reduction in reverse bending strength and/or torsional strength. According to the present invention this problem is solved by not adjusting the straightening abutments towards the workpiece until at least percent and preferably at least percent of the total energy required for heating the workpiece has already been supplied.

The invention will be more particularly described with reference to the drawings in which FIG. 1 is a schematic cross section showing the position of the workpiece in relation to the inductor, as proposed in the above-mentioned patents.

FIG. 2 is a schematic of an apparatus for hot straightening and quenching.

Referring to Flg. l, the workpiece l, for instance an axle, is mounted in conventional manner between centers and can thus be rotated about its longitudinal axis by applying torque through one of the centers. Inductive heating of the workpiece is effected by an inductor having a heating conductor 2 extending along the workpiece surface parallel to its axis and having a magnetic return 3 conventionally consisting of laminated sheet iron or pressed soft magnetic cores and a yoke 4.

The working program begins by rotating the mounted workpiece l in the direction indicated by arrow 5 and by switching on the inductor current. At a particular instant the current will flow through the heating conductor 2, for instance, towards the viewer, whereas in the yoke 4 it will then flow through the plane of the paper away from the viewer. The respective directions of the current are indicated in FIG. I in conventional manner by dots and crosses in circles. The inductor current in the linear heating conductor 2 induces currents in the workpiece which in the region facing the heating conductor flow in the workpiece in a direction contrary to the direction of the inductor current, whereas on both sides thereof return currents flow in the workpiece 1.

If the workpiece consists of a non-ferromagnetic material or if a sufficiently large part of a workpiece of ferromagnetic material has already reached a temperature above its Curie point, the inductor current and the induced current will generate forces urging the workpiece 1 away from the inductor in the direction of arrow 6. As soon as a major proportion, e.g., 75 percent and preferably as much as 85 percent, of the energy that must be supplied for inductively heating the workpiece has already been supplied, straightening rollers 7 and 8 which function as straightening abutments, and which in their positions of rest (shown in dashed outline in FIG. 1) are clear of the workpiece, are advanced towards the workpiece in the direction of the arrows 9 on that side of the workpiece that is remote from the inductor and located in positions corresponding to those in which the workpiece is straight. The forces acting on the workpiece l in the direction of arrow 6 now force the workpiece against straightening rollers 7 and 8 and the reactive forces generated as the workpiece rotates have a remarkably good straight- Y ening effect.

Reference is now made to FIG. 2 which shows a conventional apparatus for permitting the workpiece to be simultaneously hot straightened and surface-hardened. A container ll containing a quench 10 contains a drum-shaped carrier 13 which can be indexed about its axis 12, and which is equipped at angular intervals of 90 with devices for chucking up the elongated workpieces I, each such device being associated with a system of adjustable straightening rollers 7 and 8.

A workpiece 14 that is to be treated is chucked up in one such device that is in a position facing the inductor 15, rotation is imparted to the workpiece, the inductor current is switched on and-as has already been described with reference to FIG. lthe straightening rollers 7 and 8, controlled for instance by a timing delay, are advanced into contact with the workpiece. Immediately after the power supply to the inductor has been cut off-the workpiece continuing to be rotated in contact with the straightening rollers 7 and 8-the chucking device 13 is indexed 90, as indicated by an arrow 16, the heated and hot straightened workpiece being thus immersed in the quench 10. The same indexing movement carries another chucking device containing a quenched and hardened workpiece 17 into the heating station where it is taken down and its place taken by another workpiece that is to be treated.

Many changes and modifications in the above embodiment of the invention can of course be made without departing from the scope of the invention. Accordingly, that scope is intended to be limited only by the scope of the appended claims.

What is claimed is:

1. In a method of hot straightening an elongated metal workpiece having a longitudinal axis which for the purpose of effecting such hot straightening is at least partly heated to a temperature above the Curie point, comprising:

mounting the ends of said workpiece and rotating the same about its longitudinal axis,

inducing in said workpiece, by means of an inductor having heating conductors extending parallel to the workpiece axis, currents for raising at least part of the workpiece to the temperature required for hot straightening, said current and the currents induced thereby creating a magnetic field which generates electromagnetic forces between inductor and workpiece, advancing straightening abutments towards the workpiece at the end of a given heating period,

adjusting said straightening abutments to a position corresponding to the position of the workpiece when straightened so that said electromagnetic forces press the workpiece against the straightening abutments,

after the inductor current has been switched off continuing to rotate the workpiece in contact with the straightening abutments, and

cooling the workpiece, the improvement wherein adjustment of. the straightening abutments towards the workpiece is delayed until at least percent of the total energy required for heating has already been supplied.

2. In a method for hot straightening workpieces as in claim I, the further improvement wherein adjustment of the straightening abutments towards the workpiece is delayed until at least percent of the total energy required for heating has already been supplied.

3. In a method of hot straightening an elongated bent metal workpiece comprising the steps of inductively heating the bent workpiece, advancing straightening stops into contact with said workpiece during inductive heating and to straighten the workpiece, and cooling the thus straightened workpiece,

the improvement comprising advancing said stops to contact said workpiece only after at least 75 percent of the total energy supplied to said workpiece during said heating has already been supplied.

4. In a method as in claim 3, including the step of quench-hardening at least the surface of said workpiece.

5. In a method as in claim 3, wherein the workpiece is mounted axially between centers and including the step of rotating said workpiece during straightening.

6. in a method as in claim 3, including the further improvement of advancing said stops only after at least 85 percent of the total energy supplied to said workpiece during said heating has already been supplied. 

2. In a method for hot straightening workpieces as in claim 1, the further improvement wherein adjustment of the straightening abutments towards the workpiece is delayed until at least 85 percent of the total energy required for heating has already been supplied.
 3. In a method of hot straightening an elongated bent metal workpiece comprising the steps of inductively heating the bent workpiece, advancing straightening stops into contact with said workpiece during inductive heating and to straighten the workpiece, and cooling the thus straightened workpiece, the improvement comprising advancing said stops to contact said workpiece only after at least 75 percent of the total energy supplied to said workpiece during said heating has already been supplied.
 4. In a method as in claim 3, including the step of quench-hardening at least the surface of said workpiece.
 5. In a method as in claim 3, wherein the workpiece is mounted axially between centeRs and including the step of rotating said workpiece during straightening.
 6. In a method as in claim 3, including the further improvement of advancing said stops only after at least 85 percent of the total energy supplied to said workpiece during said heating has already been supplied. 